exposure indications

?? relationship between energy absorbed and signals produced

Direct, linear/proportional

mottled image is a ___ exposure

under

soft tissue and bone loss or loss of contrast is a ___ exposure

over

low mAs or insufficent # of photons

underexposure

noisy image is the result of a

underexposure

whar Maintains relatively consistent image brightness across a wide range of exposures

Automatic Rescaling- can lead to loss of visual cue relative to detector exposure

we tend to notice underexposure more than over

• Increased luminance (brightness) -

• Decreased luminance (brightness) -

lighter

darker

Overexposure (upper) leads to _____in soft tissue areas

Decreased brightness

An exposure indicator (EI) reflects???

the amount of exposure to the detector

Exposure indicator (EI)- definition

A measure of radiation reaching the detector • Numerical value reflected after an exposure

Target exposure indicator (EIT) definition

Optimal exposure to the detector • Numerical value representing the optimal or ideal exposure indicator value

Exposure ratio defintion

(EI/EIT) • Ratio of exposure indicator/target exposure indicator

Deviation index (DI)- definition

How far the actual EI is from the target EI

IEC standardized EI calculations to be ??

Mathematical equation used to calculate the exposure indicator results in a direct & proportional relationship to exposure

If an imaging system follows the IEC EI standard, then the EI exhibits a ??? relationship to exposure

direct and proportional

the relationship between mAs and EI

% change in EI = % change in mAs

EIT = 300; EI = 150; Action:

EIT = 450; EI = 900 action:

2x mAs

1/2 mAs

DI forumula

DI = 10 x log10 (EI/EIT)

how far away you were from the target value

DI

DI= what % exposure?

+3

+2

+1

0

-1

-2

-3

exposure:

100% increase (x2) doubled

56% increase (x1.58)

26% increase (x1.26)

proper exposure (x1, aka stay the same)

20% decrease (x0.8) (why? 20% decrease= 100%-20%=80%=0.8)

37% decrease (x0.63)

50% decrease (x.5) halved

If compliant with the IEC Standard, the deviation index (DI) provides a universal numeric measure of ???

how much difference exists between the target EI and the actual EI

EIT = 500, Actual EI = 250, DI =

-3